uneven bars (gymnastics)

having varying heights or levels; not flat or uniform

can't recognize tall or short (idiom); doesn't know what's what

unable to attain a high position yet unwilling to accept a lower one; caught in the middle due to high expectations

to fight it out, cross swords, or compete with someone to determine who is superior; to have a showdown

the rising and falling of the sea level; high and low water