It’s a sequence:
I’m a big fan of You can bail after you finish this interval because usually once I get through the rest valley I decide I can probably do another one.
And you’re not 
bailing in the last two minutes get it together.
Focus Paints Success.
Impossible is nothing. Is still the main one I prefer. Source was from an Adidas shirt.
When training gets mentally tough, I like to think of the phrase, “someone somewhere is training harder than you, and when you meet them at a race they’ll beat you”. Then I respond in my head, “OH HELL NO THEY WON’T”, and then I dig deep and finish. It plays to my ultra-competitive ego. That often gets shortened into the mantra “harder than you” as a reminder that I repeat at the pace of my pedal stroke.
During my last race that I won I actually summoned that manta. I thought in my head the 2nd place guy was “working harder than me” and he was gonna pass me and take the win. It kept me pushing even though I never caught glimpse of him chasing me down.
@tshortt I’ve been using this one. Motivates me to get out of bed at 4:30am and hop on the trainer by 4:45. I’ve got Kaweah coming up… 
A few things I use depending on situations (some of these echo some others above), At the end of hard intervals/workouts: “This is how you get faster!”
I have also found that form is goes a long way in big efforts, I find sitting up and loosening my jaw help immensely - I have a race tomorrow and literally taped to my top tube (where I usually tape my intervals) - “Back Straight, Mouth open!” I find this immediately helps me hit my power goals, get oxygen in and reduce RPE. I am reminded from some comments about that SMILE goes a long way as well (may need to add to top tube!).
“Discipline trumps motivation” I am paraphrasing here.
A little embarrassed to admit that I’ve looked at my iPad before the start of a hard interval and literally done this:
Other times I just say, “Bring it on.” and my mind gets right.
“Light kick! High Cadence!” Never fails to get me out from that pain zone thought. Also, I feel like I look awesome with such technique.
You didn’t come this far to only come this far.
I like “Discipline trumps motivation” too, and use it often to drag my ass out of bed. Also at work when people talk to me about knowing that they should do something, but lacking the motivation to do so. I think people are far more likely to become self-motivated when it becomes a question of their self discipline. I think we perceive motivation as something outside our control, whereas discipline is certainly ours to maintain.
Several years ago, many miles from the finish of a 110k effort, soloing into a 30mph headwind, I looked around at the beautiful place in which I had chosen to suffer. I began to sing to myself “Our God is an Awesome God”. A smile came to my face. When I think about it now, I still smile.
When I am training and it is getting hard, I remember the words of a fellow runner: “they will pay for our pain”.