Mastering both sides of the chess players

You must think for both sides. Trainers would guess that the vast majority of decisive mistakes in club play are not misjudgements but oversights and overlooking. Purdy says you will never overcome blunders by effort alone (what you need is a trained eye), which is surely true, but you must also put in the effort. If you never try to work out what your opponent might be doing, you will never find out until it is too late.