Now a proverb is a generally true statement, and I'm not suggesting that every time someone is hasty something bad happens, but on the vast majority of time - this is a true statement.
So often we want to be in on the action, and want to part of what's happening now. Whilst caught up in the moment we don't think about the consequences until it's too late.
Some of the things I've done in the past as a result of hastiness and lack-of knowledge of the situation, makes me cringe to think about, and I can think of many different (and much better) ways I could have gone about handling the situation.
There might be no immediate costs that cross your mind at first, and it's not just financial cost I'm talking about.
Relationships with those around us, spiritual relationships, personal costs, and the emotional costs. Consider it carefully, even if you consider it to be a calculated risk.
I had some grandparents who owned a chain of businesses and funeral directors, and they were offered a deal into some hotels. These hotels would have made them millionaires, however, there was only a tiny chance of the deal falling through. Even though the positive outweighed the negative by far, after my grandparents went through with the deal, it did fall through and they lost everything.
It's always good (where possible) to get someone else's idea and opinion. Don't choose someone who normally makes hasty decisions themselves and would tell you to go ahead with your plan, only stopping to think about the costs later. Instead, go to somebody who you know normally makes the right choices and seek their counsel.
You can also think about the situations of others you've heard about or know of, that are similar to yours and what happened to them as a result of their decisions.
Try to get into the habit of weighing the positives and negatives of every decision you make. This will help you make the right decisions (if you do it wisely).
First go through all the pros, thinking about them hard, and asking yourself if they're really worth it. If they are, then go over to the negatives, and ponder upon them. If you have a gut instinct that tells you that the negatives outweigh the positive - don't do it.
Also, when you're first going through the pros, and you feel that they're not really worth going along with, then don't do it.