Mistakes of Omission are the insidious ones
Warren Buffet the richest investor said his greatest mistakes are the ones were he did nothing, were he could have taken a decision but sat and sucked his thumb.
They don't show up in the balance sheets, but deep inside you know you have cost yourself a lot.
My mistakes are things I should have done, projects I should have started, Investments I could have made.
Go ahead make those intelligent mistakes, learn from it and most importantly re-invent strategies better.
Investing is something were you take action now rather than sit now and think about it later. Basically he is saying that he made a lot of investment decisions in which he did not ride on that later to be a good investment after all.