I’ve killed quite a few bonsai in my day. I’ve learned that taking too much off the plant or repotting too fast and not giving time to adjust can kill your bonsai. This is a good example of rushing the plant.
As you can see this Juniper had lots of foliage to start with. I was in a hurry for a bonsai demonstration and I skipped several steps.
I cut too much off this plant all at once. This is the finished product, but it did not live very long. I have since repented and I’m much kinder to my bonsai.