を通じて: an experience as a channel or an entire period
Distinguish results gained through a channel or experience from conditions extending throughout a period. Explore overlap with を通して and the extent of continuity within a period.
Finding the connecting channel
友人を通じて、その店を知りました。 means that the speaker learned about the shop through a friend. The friend is an information link, not a body physically passed through.
交流会を通じて、地域の人と知り合いました。 means getting to know local people through an exchange event. It names the experience or route that led to the result without saying whether that result was the original goal.
A condition across a whole period
この地域は一年を通じて暖かいです。 means that this region is warm throughout the year. 一年 is the period over which the climate is evaluated, not an information channel, and it does not imply an identical temperature at every moment.
四季を通じて観光客が訪れます。 says that tourists visit across all four seasons. Visits can be recurring events; it does not mean that the same person visits continuously without missing a day.
Comparing 通して and expressions of duration
体験を通して学びました and 体験を通じて学びました can both mean learning through experience. Because they overlap in such contexts, do not make an absolute rule that 通して is always intentional and 通じて always unintentional.
一年にわたって調査しました。 emphasizes that an investigation spanned a year. 一年を通じて気温を記録しました。 places weight on observing temperatures across the year; the exact recording interval requires further information.
Quick check: Does 研修を通じて友達ができました。 necessarily mean making friends was the training program's official objective?
Show the answer and why
No. It says that friendships developed through the training experience. を通じて identifies the route to the result, not necessarily a predetermined objective.