Motivational literature is very clear on people's need for affirmation when they're doing a good job (unlike one of my bosses who gave me a leadership portfolio and said “you won't hear from me unless something goes wrong”). Not only is it good leadership to commend people for working well, but it represents a deposit into the relational account which is one factor in building up a healthy relational bank balance.
A lot of courageous conversations amount to some level of withdrawal from this relational account, but if as a workplace leader you've been taking the opportunity to affirm people when they are working well and building up a positive relational balance, then the impact of the difficult conversation is nowhere near as detrimental than when the same conversation occurs with a low relational balance, or even worse, overdrawn.