I actually don't have the problem of lack of accountability or responsibility.
I also don't see how it relates to long term learning and efforts that make achievements such as acing college possible. The kinds of achievements that require long term discipline and work ethics.
First of all: your question says you have to fix the discipline problem as an adult. As an adult, I am assuming you're in the context of workplace, and not college.
Second - you claim to have no problem with responsibility. Maybe you have to dig into your own psychology a bit deeper (self-awareness, work against opaqueness of various parts of the mind).
The effort you put in will usually be in proportion to the seriousness and magnitude of your responsibilities. The amount of learning required to handle complex jobs is more compared to simpler jobs. Note that the concept of "learning" goes beyond mere degrees and credentials. In the real world, the best indicator for learning and competence is the power to get complex jobs done.
Say, you're managing a nuclear plant, then you need a totally different level of discipline, compared to a job where you're supposed to keep an office clean. You can mess up a cleaning job, and get away with it nobody noticing. But if your nuclear reactor goes off, then everyone knows it, and you'll not be forgiven. The demands of rigour increases with bigger responsibilities.
Aim for identifying and getting complex and difficult jobs first. If you take these jobs seriously, you'll have to transform yourself.
I also don't see how it relates to long term learning and efforts that make achievements such as acing college possible. The kinds of achievements that require long term discipline and work ethics.