The realistic version of paper trading uses real-time bid-ask data, simulates slippage, and tracks P&L the way a brokerage actually would. The toy version (which most platforms ship by default) lets you trade at the mid price with no slippage, which produces unrealistic results and false confidence. The WSW simulator uses live chains and approximates real fill behavior.
What 50 paper trades will teach you that no book can: how it feels to sit through a 40% drawdown on a long call before the stock recovers, how often you actually exit at your written profit target versus letting greed override the plan, and how reliably your strategy selection matches your emotional bandwidth. That last lesson alone is worth the time.