Conservation, choice, and the concurrent fixed-ratio schedule.

Scientists put rats in a box with two levers.

Each lever needed a fixed number of presses to drop food.

The rats could switch back and forth at any time.

The team watched which lever the rats picked.

The rats almost always chose the lever that asked for fewer presses.

A simple "save effort" math rule predicted every switch.

The animals behaved like tiny accountants counting the cheapest path.

Wilkinson et al. (1998) later tested adult humans in a similar two-button setup.

Instead of lever presses, people chose between now-small and later-large rewards.

Humans also followed a molar rule, but they tracked overall payoff per minute, not just effort.

The rat study started the idea; the human study showed the same rule works when time, not work, is the cost.

Carmichael et al. (1999) kept the concurrent schedule shape but asked if a short "change-over delay" would change preference.

They found delays did nothing; only the true reinforcement rate mattered.

Together the three papers say: learners pick the option that gives the most for the least, no matter if the price is presses, seconds, or waits.

When you set up two tasks for a client, the client will drift toward the one that costs less effort.

If you want to keep a skill in the mix, either lower its response cost or raise its payoff rate.

Check your schedules daily: a hidden high-ratio side task will lose the race every time.