The half of it
Definition 1 of 1
Pro Tip 1/3Context Matters
Understand the situation's context to grasp the full weight of 'the half of it'. 
She seems upset, but that's not the half of it—she just lost her job.
Pro Tip 2/3Hinting More
Use it to hint at additional, often complex or serious, aspects of a situation. 
His tardiness was an issue, but trust me, that wasn't the half of it.
Pro Tip 3/3Not Literal
It's not usually about exact halves; it means what's known is only a small part. 
You think this test was hard? You don't know the half of it.