1) Quick decisions are rarely good ones. Lots of people have slick pitches. Far better to wait a while, and analyze the opportunity coldly, and compare it against other ideas.
2) If I buy this, what should I sell? Not that you have to sell but it is a good exercise to make you improve the portfolio. It might indeed be a good idea, but you may have better ideas still in your current portfolio.
3) I need to analyze all opportunities through the same prism, and I need to understand them myself, not just what someone else told me. If I don’t understand why I am buying, I will not understand when to sell.
The truth is, the need for urgency in investing is overrated. If an idea is good today, it will likely be good three months from now.
Courtesy of this post from David Merkel's The Aleph Blog