...investing in yourself is self-sacrifice. You sacrifice short-term pleasure for long-term pleasure. You even sacrifice short-term success for long-term success. The long-term success is off the radar of most of your brain, so you need a mindset that sees your "sacrifice" in a positive light.
But that's not self-sacrifice by my definition, because you're still the one reaping the benefit. Getting up early to do work that will benefit someone else and not yourself - that is self-sacrifice. Getting up early to get ahead in your studies is just self-discipline.
Like I said, rationally speaking, you're right, but mind-sets don't matter when you can analyze something rationally and follow your decision without difficulty. A mind-set comes into play when a problem is rationally intractable or emotionally vexed.
But that's not self-sacrifice by my definition, because you're still the one reaping the benefit. Getting up early to do work that will benefit someone else and not yourself - that is self-sacrifice. Getting up early to get ahead in your studies is just self-discipline.