It generally takes the form of getting short term satisfaction instead of delaying gratification and putting in a bit more effort. Usually it's in response to some source of anxiety (money, or a task that's been on my plate too long), and trying to avoid it. If you're high, at least you don't have to think about your problems for a little while, right? Doing the least desirable thing on my todo list tends to be a good way to dissolve that anxiety and make me not care about getting high.
More generally speaking, life has an ebb and a flow to it. You will have times of intense work, and you need corresponding times of relaxation. Using a drug to achieve that relaxation is like eating a bag of chips to satisfy hunger - it seems to get the job done but actually doesn't.
I highly recommend talking to a professional even for a short period of time. I found it immensely helpful to have an objective, intelligent person point out my blind spots and habits in terms I hadn't considered before.
Addiction is a difficult problem to solve, and from what I've gathered from personal experience and observation, one that is difficult to overcome alone. It requires many things, including a force of will that is equal to the task of arguing against all the reasons your mind will bring to bear for getting high.
I think the book "The War of Art" has an interesting thesis on why we pursue self-sabotaging habits like drugs, masturbation or food, and I've found it helpful to read it on the bad days.