I myself find dedication a very useful way to keep me motivated.
actually, I think it is a very philosophical question. What is dedication and what is motivation.
We are in the realm of Maslow and Buddha ****.
If you need lack the motivation to study Japanese, it mean there are others needs in the lower level of the
hierarchy of needs and are yet to be fulfilled. Maybe you don't have a staple income, a good job, house over your head, enough sex, hot girlfrield, enough friends, attention and respect from people around you, etc, because all these must either be fulfilled, suppressed or ignored before you can sit down and dedicate yourself to study a language for recreation purpose.
What is dedication? May be the effort needed to fulfill one of the need in the hierarchy? And motivation powers the dedication.
Anyone here majored in psychology or into buddha/hindu life thing?
We also need to take into consideration microeconomics concepts such as marginal utility and diminishing return. In fact you know what the OP question is quite flawed, because everyone's utility function is different, hence allowing people's indifference curves to cross, allowing trade to take place. We have no idea what number of utils you would assign to Japanese compared to other activities you can do and that is different for everyone on this forum, in other words, what keeps them motivated will not necessarily work for you.