If you don’t know what to do, don’t do anything, then you waste nothing but your time and are not likely to waste any material. It is better to do nothing than to do something wrong. It affects the nerves of the boss less, as well as leaving more money in his purse.
If you do not know what is the right thing to do, and do not find out from those that do know, and thereby do something wrong, the error is yours, and you alone are responsible. It is a poor excuse to say that you weren’t told not to do it the way you blindly went at it. It doesn’t cost near as much to ask questions as it does to do the job a second time.
If you start to do a job without a clear idea of the result you wish to attain you are like a man with his eyes blindfolded going over a rocky road: you will stumble often and make many a start only to fall down again. Whereas if you have planned your job beforehand you will see the rocks in the way and go around them instead of falling over them.