Law sometimes requires formalities. Which means we have to follow them.
This doesn't just apply to wills, trusts, etc. It also applies even in litigation. For example, here, the statute that governs Section 998 offers (CCP 998, obviously) says that these offers have to be made in writing and contain a provision that allows acceptance by signing a statement that the offer is accepted. The reason for this rule is to make clear how an offer is accepted (in writing) and, presumably, to make it easy to file with the court if necessary.
The defendant here makes a 998 offer that doesn't contain a line about acceptance. Previously, the Court of Appeal had held that since the policy behind CCP 998 is to encourage settlement, we're not going to be too picky about the details. But the Court of Appeal here says, nope, on this point, the statute is clear: You've got to have that line. Otherwise the offer is ineffective. Sorry, defendant. You lose your expert witness costs.
Which is, again, a good reason why lawyers should read the statute and follow the rules therein. Or, failing that, use the forms, including but not limited to the CCP 998 form. That's (in part) why we have 'em. And it's usually even easier to fill in the blank than it is to figure out what the law requires.