Philosophy is hard stuff to read.

哲学是很难读懂的东西。

Skip the hard stuff.

跳过困难的地方。

Get the hard stuff done first thing in the morning.

早上首先完成困难的事情。

The "hard stuff" - military clout - is certainly central.

“硬东西”-军事影响力-当然是中央。

Changing ourselves, changing our behavior - this is hard stuff.

改变自己，改变我们的行为-这是困难的事情。