I think the reasons most systems go down the gurgler is that the parameters in racing are not consistent but continually change except for the following two.

Firstly, over the years horses have been found to win in direct proportion to their starting price and if adjusted for the TAB/bookmakers take, horses win rate is almost equal to their starting price. DS found this years ago and others on this forum have shown it still to be true. Hence, punters generally get a horse's chance of winning right. Its the take you have to beat.

Secondly, the strike rate for the top three ranked place percent horses is consistently just under 50% but again the take is just to much.

There may be other unchangeable truisms in but very few have discovered any that help a system.

Chaos theory shows how a small change in a single factor when repeated over and over can result in an entirely different outcome in a system from that expected historically.

I don't know how to apply chaos theory to horse racing but it does suggest why systems go wrong.