If you have cans of paint laying around which need a tongue depressor for a stirring stick, then you ain't painting non too much, huh ??
If you know your color wheel and color theory, there are so many ways to achieve the colors of your choice. Many.
It's quite obvious one needs a stirring stick of some sort, once a can has been opened. Either break through the skin and go on your merry way or just decide if you can mix the thin membrane over and have it become part of the mix once again. Before a can has been opened, they all go in our electric mixing machine. We also have electric mixers which stir up an old can of paint much faster and more thorough than a stick by hand.
For those who just stir the paint a few times and move on, you really aren't getting all the ingredients in your paint job. However, with all the additives and bullsh!t most put in to prevent drag, make time and promote this, that or whatever....... your paint today is practically worthless. Paint is basically meant to be used right outta the can. Sure, disperse it into a small cup or tin container, but if you've added thinner, penetrol, jap drier or any other additive, throw that paint away when your done with that job, because dumping that back in your can contaminates the good paint. No saving that paint anymore. To prevent this, just palette your paint with whatever additives of your choosing as you go, then you can return the leftover paint to the original can, again.