Just recently stumbled upon this puzzle so still might not understand something. Regularly I find myself in the situation when I cannot deduct concrete number anywhere on the field and, as a result, I just guess some number and continue to solve the puzzle looking if everything is ok or I move to dead-end. If dead-end then I return to the position before guessing and make another guessing.

It isn’t fun.

Am I doing something wrong or guessing is indeed a part of the puzzle solving?