The grid is an argument, not a cage
A grid does not make a layout good. It makes a layout accountable.
Columns are claims
Every column you draw is a claim about what belongs together. A grid does not make a layout good; it makes a layout accountable, because each decision now has to be argued against a structure.
Start with the measure
Set the text first. Find a comfortable line length — roughly 55 to 75 characters — then divide the page until that measure fits. Grids drawn before the content are decoration.
Name every division
A twelve-column grid is only useful if you can say what each division is for: this run of four is captions, this run of eight is the argument. If you cannot name it, you do not need it.
A grid does not make a layout good. It makes a layout accountable.
Rebuild a page you like on a six-column grid, then on a five. The asymmetry of five will force at least one decision you would never have made.