人間は持たざる時には人並みを求めるが、一度人並みになるや、今度は人との違いを求めだし、人と同じ商品では満足できなくなるからだ
At first I thought し indicated reason, but からだ already indicates reason, so し here would be redundant.
人間は持たざる時には人並みを求めるが、一度人並みになるや、今度は人との違いを求めだし、人と同じ商品では満足できなくなるからだ
At first I thought し indicated reason, but からだ already indicates reason, so し here would be redundant.
The し is just part of a normal conjugation of the verb 求め出す -> 求め出し. It would be clearer if it were written with the kanji for 出す, but when combined with other verbs it's sometimes just written だす like it is here.
You can read more about verb+出す here and here, and a little about the criteria for using kanji or not in cases like this here.