I don't believe scientific studies
More accurately, I tend to not make very large updates on the basis of studies in certain fields. A lot of people believe that if you have a study making some claim, then you have strong evidence of that claim. But they would be wrong. The mistake they're making is that they're assuming the study faithfully represents the expected data and conditioning on worlds where one would see that data. But this isn't what they should be conditioning on. Rather, they should be conditioning on worlds where they would come across a study reporting that data.
The basic problem is that if thing X has a real effect of Y, studies that try to measure this effect would report findings that cluster around a distribution centered on Y due to differences in methodology, measurement error, etc. Depending on how close Y is to zero, there would be lots of studies reporting negative results while lots of other ones report positive results. It would be very easy then to find a study claiming that X's effect is either negative or positive. So when you see a study claiming to find a certain effect, it's genuinely hard to know how faithful that is to the real one. When the person presenting this study to you has incentives to get you to believe a particular thing about the topic at hand, this is especially true.
Not all fields are created equal in this regard. Some fields are more sensitive to measurement error, methodology differences, and the other factors that lead to this problem. It's specifically in the most sensitive fields that I am as skeptical of studies as I state in the title, though I exercise lower levels of skepticism in other fields as well. So what do I do instead of relying on studies? Well, there really is no substitute for having a good model of the world. If you develop a good model, aggregated through all the observations you've come across in your life, you can get a sense for what is true and what is false that is far more informative than some random study you find.