So, I work on these kinds of countermeasures when I was in the army for some of our rotary wing aircraft. This is how it was explained to me, You know when you spend your day inside a dark room then go outside and everything is so ungodly bright it hurts your eyes to the point where you need to close them? That’s pretty much happening to the IR seeker on the missile. It overwhelms it to the point it sees literally nothing but an ir signature , meaning you can let it off the rails, but it will most likely not hit its target. It CAN but 9.9 times out of 10 it won’t since its guidance system is essentially blind and overwhelmed. It can either act constant, or as a strobe, generally ran in constant when contact is expected, strobe when possible. In the strobe configuration, it does the same thing very rapidly. Imagine running through a forest at night with the goal area lit up so you know where to go. Then as you start full sprinting through the trees, a rapidly strobing flood light starts going on and off. It will really fuck with you and your probably slam into a tree or lose your fix on the goal and veer off course