Never underestimate the impact of a big bunch of flowers and a pot of basil by the sink.
The Sun
And you can't underestimate the impact that can have.
The Sun
People with low self-esteem can often underestimate the impact their actions can have upon others.
The Sun
Stating fees in annual percentages encourages investors to underestimate the impact of charges.
Times, Sunday Times
Also, don't underestimate the impact letters of thanks can have on morale.
Times, Sunday Times