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You have fallen victim to the common misunderstanding about MBTF, which is perpetuated by the industry.

The error is partly due to the fact that the units are incorrectly stated. The units of MBTF are something like "unit/hours".

MTBF is a measure of how many units will fail in a given amount of time. Thus, a MBTF of 100,000 says, "out of 100,000 units, one unit will fail per hour." This is a useful measure for planning the number of replacement parts necessary (in rather large environments perhaps).

Some examples, a battery which might only last a couple hours, might still have an MBTF of 100,000. Of 100,000 batteries, one battery will "fail". All of the (other) batteries still will only last a couple hours.

Another example, men, aged 30, have a MBTF of 1000 (roughly). Out of 1000 men, one man will die. However, to the best of my knowledge, no man will live to be 1000 years old. As stated, MBTF is a useful measure for stocking purposes, or in this case with men, women need to keep approximately 1000 men "on hand."