What triggers the second wave of Corona attacks and is it really getting lighter?

Some countries are now reporting a spike in new cases after easing restrictions or lockdowns. As happened in China, the surge in local Corona cases was reportedly centered in Beijing.
However, what is the second wave of Corona like? Will it be the same as what happened in the first wave, or worse than the previous one and what triggered the second Corona wave?

Quoted from the BBC, the following explanation:

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Will the second wave be the same as the first wave?
Dr Adam Kucharski from the London School of Hygiene and Tropical Medicine explained the second wave of Corona had the possibility of lasting longer. This is because there are still so many people who are susceptible to Corona virus infection.

"(But) if the Corona case rises again we can reintroduce a strategy to suppress the second wave, it is always an option available to us," said Dr. Kucharski.

What can trigger a second wave?
The expert said that what could trigger the second wave of Corona was ignoring the restriction or loosening the lockdown too far.

"The ultimate puzzle (the strategy to deal with the Corona pandemic) is how to maintain control, while minimizing disruptions on a daily basis," Dr. Kucharski said.

The expert said that is why the steps to relax the restrictions were carried out gradually and new ways to control the Corona pandemic continued to be implemented, such as contact tracing and wearing masks.

Will the Corona virus be lighter and no longer a problem?
Allegedly the second wave of Corona appears to be no more dangerous than before. The theory is that the virus will spread even further if they do not kill the host and become lighter.

"But that's not guaranteed, this is a bit of a lazy thing done by some virologists," said Prof Ball, a British expert.

Mentioned, more than six months into the Corona pandemic, there is no clear evidence that mutated viruses spread more easily or become less deadly.

"I think the virus is going very well now. People often have very mild or asymptomatic infections, if they can transmit then there is no reason to imagine coronaviruses need to be lighter," said Prof. Ball.