More: if really people are going away because they find advancing too difficult (and only a poll can reveal this), the solution doesn't need to be so drastic as making loss impossible and advancement certain. There are compromises. Requiring two losses for a rank-down could be one. If that isn't enough (though to me it seems already too much), we can require two
consecutive losses.
Warning: the following statement wasn't verified. And I failed my Statistics exam this semester

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The latter choice would (statistically, on a huge number of fights) have about the same effect as your proposal.
edit: hmm, let's see. If you lose with two consecutive losses, on 2 fights (after a win) you have 25% of losing, 50% of going up once, and 25% of going up twice. On 2 fights (after a loss) you have 25% of losing, 25% of staying, 25% of going up once, 25% of going up twice.
With no losses, on 2 fights you always have 25% of staying, 50% of going up once, 25% of going up twice.
Ok, the previous statement
is officially screwed.
