when do we realise its a wrong investement?

often we invest..invest in many things..invest our money in equities, MF, FDs, real estate and also invest in non monetary stuff like friendship, relationships and also time
and in real value terms the last investment is the most valuable thing that we invest, the time.
so when does we realize that the investment that we  made was right one or a bad one?
what would be the ideal time that makes u realiz this? the sooner the less the damage?
but some times a little damage is enough to make it irreparable.. a wrong step taken was enough to prove it was the wrong investment..making the first step right was important? ain't it?