One of the fields I work on is computational complexity. Accordingly, met people tend to tackle first the easy problems, and leave behind the difficult problems. The trouble, though, is that many times the most crucial problems are the ones we usually leave behind. In any field of science, or life.

Thanks to All and I am agree with your experience to handle the problems.

@ Carlos,Dear Sir ,

I am totally agree with your last line "The trouble, though, is that many times the most crucial problems are the ones we usually leave behind". Most of times,after solving a problem, I realized  that solution was just a step ahead, when I had left that. this is also true in our daily life as we are full of mistakes. And we always think to improve mistakes,like "wish it had happened or wish it had never happened or wish this and that etc".  I don't know, how could we avoid such silly mistakes or how can we improve such things in life and also in research work to solve problems properly?"I would like to say our mistakes are creating more problems for us".