In my humble opinion, the strongest motivation is comes from anger, and then love. My previous post on emotions I have stated that Anger allows someone to totally focus their thoughts in one thing and one thing only. Of course, anger without control will make you not think properly, however, anger leading to revenge fuels motivation. While it's quite common for people to spend a lot of time plotting revenge due to anger, this can be turned positively. So, well, revenge is not that bad now, isn't it?
But how? Bringing an real life example here, while it's VERY minor and not at all life-changing, at least the example will show how such revenge can create motivation. Personal life, during studies, I have never been motivated in History and Additional Maths. For History, I personally do not favour it, while for Additional Maths, I only truly learn that which I think I will use in life, therefore things like Trigonometry is something I'd never paid any attention.
In both subjects, my teachers were very aware of my "inability to master" the subject, and have been subjected to snide remarks or criticism. Once my Add. Maths teacher asked me to answer a question, when I couldn't, she said "Well of course, why did I ask you? You are never good at Add Maths." Anger. Of course, angry! So what now? Smash the teacher's car windscreen? Empty out the teacher's car tyres? The answer is revenge! But what type of revenge is considered non-crime and non-hurt? Letting the teacher eat her own words. So there.... I plotted my revenge.
But it was not a revenge at all. Since both teachers had look at me as a failure in their subjects, the least I can do is show them that they're wrong. The revenge motivates learning. True enough, the next exam for the subjects I took, I scored 100% for History and have 96% for Add Maths. The feeling of "See what I can do?! Now I showed you!" Teachers shocked, anger ceased. Teachers asked why not I maintain my grades, I told them I learn what I like. However.... because I really DO NOT LIKE learning them, following exams brought me down to my usual 40% - 60%. It's just to show that while you're angry, you're motivated.
This brings to various other examples in comics, or even in real life. Okay, let's not cover real life. There's way too many stories from Mohamad Ali, to Warren Buffett. Like it or not, if you read about them, there's always an element of anger from stress/frustration that motivated them. One story in Archie comics that we all can relate to tells a story of when Betty was competing for a swim meet. While it was difficult for her to be champion (due to not having a determined bone in her body), she focuses and channel her strength well when she gets angry. For that to occur, Archie and his friend pushed her coach into the pool in a joking gesture that got her fuming, angry that she focused her anger and energy, to end up winning the competition.
Don't underestimate comics or any other leisure entertainment we see. They are real life stories within it. If just say, one is driving to a race meet, and encounters some anger on the road (due to other drivers' actions drives one crazy), one can channel one's anger into the race, and "change" the anger into fuel for energy. Career? Same. Realistically, you are actually more attentive and focused when you are angry, therefore, channel it to work.
Two of the bravest people in the world are a person in extreme anger, and a suicidal person. If you end up angry, find a way to channel it to revenge, and then to motivation. The revenge is not ON the person, but you revenge against your own weakness when you are not angry. Anger is energy.... same as any other energy ie. nuclear, sound, motion. If we learn in physics that energy transforms from one form to another, so can emotions.