“I've taken stuff from people, too. You know though, if you steal from one person, you're just a thief. But if you steal from everyone, that's research.”

Source: A Face Like Glass

Source: The City of Dreaming Books

Sharpe (Novel Series), Sharpe's Escape (2003)
Context: Until two days ago,' she went on suddenly, 'I thought that my life depended on other people. On employers. Now I think it depends on me. You taught me that. But I still need money.'
'Money's easy,' said Sharpe dismissively.
'That is not the conventional wisdom,' Sarah said drily.
'Steal the stuff,' Sharpe said.
'You were really a thief?'
'Still am. Once a thief, always a thief, only now I steal from the enemy. And some day I'll have enough to stop me from doing it and then I'll have to stop others from thieving from me.'
'You have a simple view of life.'
'You're born, you survive, you die,' Sharpe said. 'What's hard about that?

Source: Going Postal

Source: Tell-All

As quoted in Tesla : The Modern Sorcerer (1999) by Daniel Blair Stewart, p. 411.
Date unknown
Variant: Everyone steals in commerce and industry. I have stolen a lot myself. But at least I know how to steal.

Source: Othello

Source: Pale Fire