what does "scalable" mean in this context?
It’s easy to carry those bad learning habits into working life, reviewing the key materials for a big meeting just an hour beforehand, or staying up the night before to prepare for a presentation.

But this approach is neither sustainable nor scalable. In my consulting work at the NeuroLeadership Institute (NLI), I meet countless employees at hundreds of companies who are drowning under the weight of all the new skills and processes they’re asked to pick up quickly and completely, remember, and then put into practice. It’s a surefire recipe for burnout and ever-falling productivity.

"But this approach is neither sustainable nor scalable."
I don't understand this sentence.

Question

what does "scalable" mean in this context?
It’s easy to carry those bad learning habits into working life, reviewing the key materials for a big meeting just an hour beforehand, or staying up the night before to prepare for a presentation.

But this approach is neither sustainable nor scalable. In my consulting work at the NeuroLeadership Institute (NLI), I meet countless employees at hundreds of companies who are drowning under the weight of all the new skills and processes they’re asked to pick up quickly and completely, remember, and then put into practice. It’s a surefire recipe for burnout and ever-falling productivity.

"But this approach is neither sustainable nor scalable."
I don't understand this sentence.

Answer

the approach is not sustainable = last moment preparations are not good habits to have for 40 years in a career. You did it as a student, but it cannot succeed/it can't be repeated forever, this tactic.

Scalable = to scale up. To take a plan or a model, and to make it bigger, to make it on a bigger scale. The approach is not scalable = The approach you had (i.e. the bad learning habits), is not able to cope with the demands of a normal career, it can't be made bigger to solve a bigger task. I.e. learn better study habits, that are better for all of your life and career. Staying up at night to study something, is not a good habit to do in your career for a few decades.