Mackay told BBC Three Counties Radio: "If you're playing well and scoring goals, that's when you've got to keep believing that it will come.
"You give that belief to [the players]and say, 'there's your evidence - keep playing like that and this changes'."
The victory against the Foxes was Watford's first since 19 October, when Ipswich Town were beaten 2-1 at Vicarage Road to send Mackay's men third in the table - they are now 10th.
Mackay has had to turn to youth this season as financial restrictions have limited his ability to bring in players.
Of Watford's 18-man squad at the weekend, 10 were aged 22 or younger, and the average age was 24.4.
And their manager is hopeful they will become better players after helping end their side's poor run of form.
He said: "This is what gives you that experience to build on.
So I was very pleased to see Buckley start on Saturday. I think he offers pace and a freedom to the play
WFC
"Jordan Mutch in the middle of the park [is] another one who, because of his size and height, people forget is 19 years old.
"Will Buckley [is] another youngster - all these experiences are going to be great for them. This is the first year in Championship football for some of them and it's something that will stand them in good stead for the future."
Watford next travel to leaders QPR on Friday looking for their first away win in over two months.
Source: BBC Sport
Source: BBC Sport