The difference is clear, investing what you can afford is used when you are interested in building future wealth while investing what you can afford to lose applies to cases where you just want a short-term profit and it mostly happens when you're trying things out.
I disagree. Even with long-term investing, it is good practice to only invest what you can afford to lose in the short term. Markets fluctuate, and even solid investments can experience temporary dips.
The concept of "afford to lose" depends on more than just income levels. For instance, an individual earning $200,000 annually may not actually have the flexibility to risk $40,000 if that would disrupt their overall financial security. The total financial picture matters - factors like existing debts and future needs should be weighed when deciding how much can reasonably be put at stake.
And I really wouldnt compare investing to gambling in any regard. They are fundamentally different financial activities with vastly different risk profiles and outcomes. Conflating the two does a disservice to the practice of thoughtful, research-based investing.
We don't invest into something and yield bad outcome in our thinking, a good investor will always even at his lowest remain positive to his investment, this is where it sits the difference between gambling and investments. We gamble with what we can be able to lose because our chances of getting profits from it is limited, so we deploy such methods in order to be on the safe side. Whereas In some scenario like more of a physical investment one can invest with a lot more than he can afford to lose because it's a very rare possibility of the investment collapsing. For example, building a house for rentage which we know the drag associated for owning one, what will be probability of finishing the building and not having no one to rent out the house. But in a good sense, and some specific investment deserves a compilation of both to be successful.