England are fifth in the group standings with one win from three matches after the 69-run defeat, having been thrashed by New Zealand in their opening match. The top four at the end of the round robin phase advance to the semi-finals.
Buttler said the Afghanistan result was a "big setback".
"Before the tournament started we had a different idea of how the first three games would pan out," he said.
"We’ve got to show a lot of character, a lot of resilience within the team and most of all a lot of belief.
"There are a lot of excellent players in there and we haven’t played well enough today, but we must keep that belief."
Winners of the T20 World Cup in Australia last year, England hold both the global white-ball trophies but have yet to impress in the subcontinent.
Buttler conceded the England brain trust had misread the pitch and the conditions, retaining an extra seamer after seeing India beat Afghanistan at the same Arun Jaitley Stadium last week with a similar attack.
"Obviously India went with the extra seamer as well and we thought the wicket would play similarly and maybe the dew would come in in the second half," he added.
"The conditions didn’t play quite as we thought they would ... The wicket didn’t play exactly how we thought it would play and the dew didn’t come in as much as we thought as well."
Chris Woakes's struggles continued, the seamer conceding more than 10 runs an over and sending his first ball down the leg-side and through wicketkeeper Buttler for five wides.
Buttler said Woakes had not bowled at the level he was capable of but would not be drawn on potential selection changes ahead of their next match against undefeated South Africa.
"We’ll let tonight sink in and work out where we need to go from there," he said.
