Instead of saying that, “I don't think so” or “impossible situation” or “difficult task” etc. we may try by saying, “Why don't we try to do things in a different way?” “How about giving it a shot?” “Why not?” and “let's make an attempt at least!”
By inserting the seed of positivity, we are trying to bring in the “possibility” factor to the job in our hand. Who knows, we may end up in completing the job as well!
However, nothing is going to change our situations, neither by being negative nor by being positive, and hence, why can't we be positive?
There is something wonderful in being positive under all the circumstances.