The Mishna 4:12 says "Im Batalta Min HaTorah Yesh Licha Biteilim Harbei K'Negdecha"; literally translated to mean, if you neglect Torah learning you will have much wasted time against it. Rav Shlomo Kluger explains, in his sefer Magen Avos, that people think if they study a profession or open up a business they will profit greatly. This is true if they are the only ones with this idea. However if everybody chooses the same profession there will be a glut in the market and then there is no guarantee that they will even be able to earn a living.
Therefore the Mishna tells us, if you stop learning Torah and choose a profession you should know that there are many like you and you are not guaranteed to realize your dream. However continues the Mishna, "Im Amalta BaTorah"; if you toil in Torah even if there are many like you that all choose to learn Torah you are sure to earn a big payback because "Yesh Lo Schar Harbei Litein Licha"; Hashem has no shortage of reward to give out to all those who learn his Torah.