Don't build a castle; put up 1,000 tents.
Vince Stehle gave me this advice on more than one occasion while I was serving as the first Executive Director of the Nonprofit Technology Network and he was a member of our founding Board of Directors. I consider myself privileged to have had Vince as a mentor, and this is one of the most important lessons he taught me.
The implications are clear: Don't over-invest your resources (time, money, attention) in a single, grandiose enterprise. Instead, experiment across a portfolio of possibilities, and double down quickly on the ones that show promise. Beware of commitments that will make it difficult to alter course in the face of changing conditions. Instead, be nimble and responsive to incoming data (and resist the gravitational pull of sunk costs.) Finally, don't prepare for siege warfare when all you need is a little shelter from the rain.
To be sure, the applications--the precise situations in which we should apply these heuristics--can be fuzzier, and this is where life experience, pattern recognition, and honing our instincts are key. Because sometimes we do need to make a single, big investment, and embracing that portfolio of possibilities will spread us too thin. And sometimes we have to be committed for the long haul, and if we cut and run we'll miss the success that was just around the corner. And sometimes--every once in a while--we really are besieged, and nylon mesh won't stop cannonballs.
But I've found that Vince was right more often than not, and checking my impulse to start castle-building and diverting those energies into putting up lots and lots of tents has usually proven fruitful. (Of course, there's a useful tension between this dynamic and my persistent perfectionism, and sometimes the latter gets the best of me.)