How often to units deviate from scripts?

[Debaser8]

My stupid Kinara cast a 100 fatigue wind guide when he was supposed to be holding. He then followed his next order, attack archers, to the letter, which resulted in him becoming mute. How often to commanders deviate from scripts and what can be done to prevent this? He probably shouldn't have had an air gem, but I was hoping he would use it to reduce mistform's cost.

[Debaser8]

He cast the wind guide instead of charge body, which he had from his copper plate, doh. I wish the AI would take account of fatigue when selecting alternate spells on thugs that are scripted to attack.

[WingedDog]

In your case I'm pretty sure Kinnara was scripted to 'Hold or cast spells'. Commanders never disobey 'Hold' order.

The most popular reasons for commanders not casting spells they were scripted to are:
1) No targets in range of scripted spell;
2) Commander was scripted to cast a battle enchantment or some spells like returning, and enemy army is too small by AI judgment (a single scout for example).

Edit: Ninjad.

[13lackGu4rd]

as for your ogiginal question, how often, generally if your scripting is good than never. however scripting can be faulty for a variaty of reasons: no targets in range, forgot to bring gems to commanders(for spells that require gems that is), already having the effect(such as your charge body example), the enemy being immune to your spell(like scripting cold attacks against an all undead army), etc.

[Illuminated One]

The having the effect can also be in place when you only technically have the effect with not enough to benefit.
For example if you script an eagle king (100% shock resistance) to ironskin (-75%) they have 25% shock resistance. Meaning still toast in one hit. But they will ignore any order to cast lightning resistance. Don't know if that's limited to lightning or to units starting with 100%.