A recurring problem in sessions is that instruments fall out of synch, off-beat, or whatever you want to call it.

Greg Stephens pointed out that orchestras and such things have conductors who dictate the beat, and, in fact, smaller ensembles without conductors generally take the beat from a drummer, bass player, guitar, piano, or other chordal instrument. That is, in fact, the major role of a chordal instrument in any ensemble.

The thing is, in sessions, the lead player often sets the beat and everyone else, including the chordal/rhythm instruments is supposed to follow. "Follow" of course means that the nearest players get to the beat slightly after the lead, and the next nearest players get to the beat slightly later than the nearest players.

The effect is the same as that of a traffic jam, where the first driver hits the brake for a second, the second sees the brake lights and hits his brake for two seconds, and ultimately, a mile behind, everyone grinds to a standstill--