"Positive momentum is when things start to go well for you, and everything helps you continue and succeed more.
Imagine you are rolling a ball down a hill; the moment you start pushing it a little, it moves slowly... but as you keep going and increase the speed, the ball gets bigger and moves faster and easier. This is momentum.
In life or work:
When you start working towards a goal and achieve a small success, that success gets you excited.
Excitement makes you work more.
Your work increases the chances of success.
And your success increases your excitement even more… and so on.
So, positive momentum is a "good cycle" that starts small and grows over time, and every positive step pulls behind it better steps.