I always play cognitive tricks on myself.
1.) ‘I never quit a workout without starting the next interval’
2.) ‘If I start an interval I always go a least halfway through it to see how I feel.’
3.) ‘If I’m already halfway through an interval this is really just where the payoff starts. I don’t want to go through all that discomfort to get back to this point again. So make it count now.’
Also, I have about a half dozen race memories where I got dropped at a critical point, or a hated rival got the best of me, or I lost a time trial/podium spot by a couple seconds. Spots where it really mattered if I had just a little bit more. If things are really hard I’ll try to re-live those in my head knowing that if I could just push through those moments outcomes would skew heavily towards success.
It sounds screwy, but sometimes just making yourself smile and chuckle a little bit helps. YMMV on that one.