The Irish (my heritage), fought against the English occupation for roughly 800 years.
In one way, that is admirable. Yes, they never gave up. But also, they never won.
How can you fight an 800 year war and never win? Because for 8 centuries, they fought the British according to the British style of military engagement. Large-scale battles, in strict battalion formation, army against army. Irish rebels tried to act like a formal military because that is the only way they could imagine armed struggle.
When finally a visionary IRA strategist named Michael Collins emerged after the disastrous Easter rebellion of 1916, he completely overhauled the volunteer fighters into a fluid, mobile guerrilla army.
He established what were called “Flying Columns”, squadrons of between 25 and 50 men who would dress in civilian clothes, and be in constant movement, ambushing British convoys, attacking bases, checkpoints, and so on.
He developed a network of informants to provide information about the identities and activities of British intelligence agents and their spies. Finally, he organized teams of volunteers to assassinate those agents.
The IRA, after 800 years of defeat, succeeded in driving the British out of all but 6 counties in Northern Ireland within 3 years of adopting these new tactics.
The point here is not so much about the particular strategies developed by the IRA under Michael Collins; the point is the unparalleled importance of flexibility and adaptation.
There is nothing more important than ability to free yourself from dogmatic ideas about what form fighting should take, so that you can devise tactics to fit the circumstances.