Robotics is a very large field, covering everything from battlebots to putting robots on mars. FIRST is a good way to learn the basics of engineering and robotics but it is by no means the end. Everything different that I work on i look at it as an application of knowledge that i have acquired and also a learning experience and if opportunities are presented to me to work on challenging projects i always go after them. I think it is important for people to expand their horizons and try new things.
From personal experience I just recently built a battlebot and while there were alot of similarities between the FIRST robots i have worked on and the bot it still exposed me to some different applications of technology that i would never have seen otherwise, even stuff i may use in FIRST in future years (no spinning weapons though
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Just remember that FIRST is just the beginning of what you can do if you put your mind to it.