Why fees jumped on Tuesday, and why most people did not notice

Fees for an ordinary payment on one network rose several times over for about six hours on Tuesday afternoon, then fell back (sample report, 5 of 6 checks: developing).
The reason is space: each block holds a limited number of payments, and when many people send at once they offer more to be included first. Payments with lower fees simply waited a few hours.
If a payment is not urgent, a lower fee usually gets through within a day. The amount you send does not change the fee.