If you can't figure out motivations, then you don't yet have your interesting character as far along as you think. You have a portrait, a moment in time, not a live person who will stumble along tripping over himself as well as external problems.
Give him backstory. What is he afraid of? What incidents in his childhood/adolescence still make him wince when he wakes up at 3 am and (unwillingly) remembers them? What does he wish he'd done instead? Why? What does he yearn for? Does he understand himself at all, or is he going to be blindsided by parts of himself he doesn't recognize? What makes him really angry--losing-control-angry? Does he know that will make him that angry? (Characters surprising themselves make good story.) Which of his traits does he most value and depend on...and what is the stress that will make that trait unreliable? Then, of course, you apply that stress somewhere in the story (in the right place. Which is the art of plotting.)
Poke and prod your character until he's moved to DO something. And have that something backfire. He's late for work because (??? alarm didn't go off...because??? there as a power outage???) and he hurries, thinking he can get there on time, and chances a caution light, but it turns red and he's stopped by a policeman...now he's really late for work, so he calls and tells the guy at the next desk to tell the boss there was a power outage in his neighborhood. But the guy's been competing with him for promotion and instead says to the boss (who says "Where's Henry?") "Oh, well, Henry...I think he had a problem..." in that tone of voice that implies Henry is often late and comes in red-eyed and bleary from a night on the town. Henry has allergies, and does often have red eyes, so when Henry comes rushing in, and steps on something that slips, what the boss sees is reliable old Henry staggering and red-eyed, and...there's a start. There's the conniving fellow at the next desk, but Henry doesn't know that he misled the boss...so he doesn't know he needs to do anything....he doesn't understand the boss's tone when the boss says, "Power outage this time, eh, Henry?"
Remember that the character's problem can be internal (he's his own worst enemy) as well as external, and that the common forms of bad behavior can cause just as much grief as giganto-monstro-towering-evil-in-black-cape kinds. Ambition, greed, cowardice, arrogance, dishonesty, laziness, boredom (the bored child will get into trouble, and so will the bored adult), desire for revenge (often executed against the innocent) etc. And on the good side, any "good" trait without judgment. (In the current group of books, two rulers, each convinced he is Right, and traditional enemies, discover that their definitions of "right" are perpendicular to each other. They aren't even on the same axis. I personally would rather hang around with K- than T- but T- isn't evil. But in his ignorance, and operating on assumptions that are false, he is capable of great harm. OTOH, part of his misinformation comes from someone who is evil, in the traditional sense--a troublemaker who likes to spread death and destruction.) There are such people in this world, so it's realistic to have one of those around now and then. They usually operate by misleading people, stirring up hatred and violence.
But mostly--deepen and complicate your characters. Until you have motivations, you don't have movement--action--behavior--and if you find you have behaviors, then you need to dig out the motivations behind those behaviors, to your best understanding of how humans operate. Look at real people; look at yourself; read news stories about individuals and consider motivations for them (not always the obvious motivations, either...not the assumptions you came in with.)
When your characters are ready to act--leaping into action--then it's time to consider plotting. Start with Aristotle. Nothing's changed in human nature since then.
