"曲折的学习经历" in English? How will you say "曲折的学习经历" without negative connotation? "torturous experience" is one that involves pain, suffering, or discomfort, and does it indicate some negativity?

For example, a graduate student who had to change his study focus twice, and hoped that he could eventually switch to the research area he loved. 


  Because of his 曲折的学习经历, he more treasures the opportunity that he can have.


How about"坎坷的学习经历"? Will it be more appropriate and easier to translate into English, than "曲折的学习经历"?

If if were you, how would you say the above in English?

Thanks!
曲折的学习经历= step-by-step experiences of learning/(properly) gradual advancing in learning.  

坎坷的学习经历= troublesome experiences of learning

Since 经历 is equivalent to experience's'   in English, it must be step-like. Thus we shall focus on the secondary meaning of the adjectives.