INTPs are the idea mills of the personality world; always examining, always questioning and always musing about some theory. They live in a world of "what if" and possibility. When there's really no answer, INTPs are the most interested.
But often, "what if" is a double-edged sword. On the one hand, it's a clear strength that you're able to keep your options open. You wouldn't be able to philosophize, categorize and objectively analyze the possibilities before you if you made snap decisions based on half the facts.
On the other hand, your tendency to question the validity of everything means you're never truly certain of anything. In a job, you worry that you're on the wrong career track. In a relationship, you worry that you might be happier single. In social situations, you worry that you're saying or doing the wrong thing, and there's usually a significant amount of shame when you decide that yes, you could have made better decisions and the grass is probably greener on the other side.
What gives? Why does the idea of making decisions eat you up so, and how do you stop yourself from second guessing the decisions you have made? Here are four suggestions.
#1: Accept that there will never be enough information.
Some INTPs confuse their tendency to second-guess themselves with a fear of failure, but it's not that at all. The reason you second guess yourself is that you see the absurdity of acting on limited information. Getting into action when you don't have all the variables goes against your instincts - it feels rash and foolish to you.
So let's start with a realization: you will never have all the information. It's great that you're concerned about the logic and accuracy of your decisions, but you cannot predict the "should haves" any better than I can predict the start of World War 3. We're not omniscient. We just have to work with what we have and take those risks now and then.
I know this is a typically INTJ thing to say. The fundamental difference between us is that I take only the data I need to create a comprehensive plan, while you keep on info-gathering. And your decisions are likely much better quality than mine. But the fact is, positive change won't occur until you stop looking for data that doesn't exist and actually accept the cards you've already got.
#2: Get an outside perspective.
One thing all INTPs realize as they get older is that it really is helpful to talk through problems and get an outside perspective. You like hearing the thoughts and ideas of others, and while home truths can be a little hard to take at times, you're the first to admit when you need a reality check. Sometimes even just speaking things out loud can break the vicious loop of overthinking and give you some acceptance.
#3: Make a decision. Then make it right.
You're going to make mistakes - that's a fact of life. You might think that being wrong is not an option but reality check: it's inevitable, for each and every one of us, regardless of type. So don't second guess a decision just because it might be imperfect. Playing safe or worse, throwing your babies out with the bathwater, leads to mediocrity. Taking risks, on the other hand, pushes you into territory that could lead to your biggest wins.
There are such things as course corrections. In time, you'll have the opportunity to fix all sorts of things you might have screwed up. But you never know where your decision will lead you until you've made it. The outcome is the bit that comes after the decision. Never before.
First, make the decision. Later, you can work on making the decision right.
#4: Don't fall into regret territory. Learn.
If you were a value-driven personality type, an INFJ for example, you could start from the perspective that the path you choose to walk is the important thing. But you're not one of those types. You're an INTP and for you, it's not the path that matters but how you choose to walk it. Every path has possibilities. Which one you wind up on is not as important as what you can learn and explore along the way.
What's curious about your type is that you have such an eyes-wide-open, playful approach to learning, yet such as glass-half-empty, pessimistic approach to decision making. What would happen if you reframed your decisions as learning experiences? Could you transfer some of that playful curiosity to your decision-making, and stop being so pedantic?
It's fine to look back and consider if, in retrospect, the decision you made was the right call. This is valuable feedback for your future decision making. Just don't fall into regret territory it if it turns out to have been the wrong decision. Nothing is irreversible. The situation doesn't have to stay that way forever. Accept where you are now, do what you can within those boundaries, and do what you do best. Learn.