You conclude, incorrectly and without considering other alternatives or testing your assumptions, that you understand how another person is thinking and what their reasons and motives are for taking a particular action. This is an example of the Fundamental Attribution Error where you incorrectly attribute an action or intent to an agent. One example of this is drawing a negative conclusion in the absence of supporting information. Focusing only on evidence that supports a negative position, while neglecting to consider alternative positive explanations is the fallacy of not considering representative evidence.
First of all, why would you want to know what someone's reasons are for behaving in a certain way? Ultimately, it's the consequences of their actions that affect you, but predictability is also important, especially if you should interact with this person on a regular basis. And you can't estimate the predictability of their behavior solely based on consequences, because there are external factors that may have been a major influence, as well. In short, we need context in order to more objectively judge a person's behavior and estimate its probable occurrence in the future. Accurate judgment helps us prevent bad consequences and maximize good consequences. Hence, it is in fact very useful, in the long term, to know why people do what they do, in case you plan on interacting with them on a regular basis.
People fear the unknown. If they lack context, they make shit up. Optimists assume you didn't say "Hello", because you didn't see them. Pessimists assume you hate them. Some who try to be objective consider both options and can't decide which one they should go for, which makes them even more anxious. They're like, "It's more probable that he didn't see me, but what if he does hate me"? So clearly popular cognitive psychology fails in their approach of solving the issue of Mind Reading. They suggest that for every negative example that pops up in your head, you should think of a counter example; a "rational response". To me, this is simply a waste of time and energy.
Here is my approach: when in doubt, think about whether it's within your control to find an explanation. You can't know everything, because you are a limited human being. If it's not up to you, don't bother thinking about all the possible options. If you don't know why somebody did something, and you have no evidence to back up any claim, you can simply accept that you don't know, and ask the person why he did it as soon you get a chance. Embrace your ignorance. Let go of religion. What do you want? Made up knowledge, or real knowledge? The fact of the matter is, you don't know. Being aware of the context is useful for maximizing predictability. When the context is false, the whole point is lost. If I want to know how rockets are constructed, I can think of a hundred possibilities, and they'll probably all be wrong, because I'm not a rocket scientist. I'm better off trusting the latter, even though there's a possibility that they could lie to me.
There's this potato chips factory. You felt sick after eating their chips. What happened? You have no access to the product ingredients, and there's no way to know what's inside. If you assume that the ingredients are poisonous and you turn out to be wrong, you might miss out on some great tasting product. On the other hand, if you assume that the product is healthy, you may get sick again. You could assume both are plausible options, and take no action. The owner of the factory claims that there is nothing unhealthy about his product's ingredients. You can't fully trust the owner of the factory, because he has the incentive to sell his product; he wants to advertise it to you. There's good advertising, and there's deceptive advertising.
When you have no evidence against the owner's claims, you have no other choice but to either reject the product, or initially trust the owner. It's more probable that you get the truth from him, than from your blind assumptions. If it turns out that he lied to you, you could simply choose to no longer trust the owner and discontinue consuming his product. Trick me once, shame on you, trick me twice, shame on me. So did the owner lie to you, or was it something else that negatively influenced your health? You initially trust him. Later on, you decide to buy potato chips from his company again. Same thing happens - you catch diarrhea. Well now you really have a reason to doubt the owner's credibility. You buy his product one more time - diarrhea. Now you have enough evidence to make your own judgment about the ingredients, and conclude that there's something in these potato chips that is detrimental to your health.
The factory manufactures a product, the same way a person's brain provokes his actions. When you interact with someone, his behavior is the product that you consume. The ingredients of the product represent the person's thoughts that lead to his actions. And if you want to make sure the product is good, you should know what the ingredients are. Overall, you shouldn't fully trust the owner. Listen to his opinion, but ultimately trust your own judgment, depending on how his product makes you feel, and also considering his previous products. So if someone often hurts you in a certain way, but he claims his intentions are good, he is lying that his product is harmless, because objectively speaking, his product does seem to poison you.
Sometimes a company would produce many products, but only a few would be bad. It's up to you to decide whether you want to boycott the company, or simply choose to avoid those specific harmful items. Sometimes compromise is better than boycott. If the company overall produces superior quality products, it will not be a beneficial decision to refuse their services because of a few bad apples.
