One step short of something; just before reaching a particular state or event—on the verge but not yet there.
成功の一歩手前であきらめてはいけない。
Don't give up when you're one step short of success.
事故の一歩手前でブレーキが間に合った。
The brakes stopped the car just short of an accident.
商品化の一歩手前まで試作品が進んでいる。
The prototype has progressed to just before commercialization.