Depression isn't laziness—the brain miscalculatesHow mental disorders play havoc with our motivation

The "lack of motivation" in mental disorders stems from an imbalanced cost-benefit calculation in the brain, not weak willpower.

Replying to a message, taking a shower, going shopping—these small tasks can feel overwhelmingly hard for some people. Others say "You're just lazy," but the problem may lie in an invisible calculation in the brain.

Scientists break down the moment of decision: the brain constantly calculates how much effort an action will cost, how much reward it will bring, and how likely that reward is to arrive. Only when the math feels worth it do we act.

Mental disorders throw the math off

A meta-analysis of 68 studies found that people with schizophrenia, depression, or bipolar disorder are less willing to exert effort for rewards. When the reward increased, they didn't ramp up their effort like others did.

A healthy person who sees the prize go from $1 to $5 might press the button more. But those with these diagnoses stay unmotivated even when they know the payoff is bigger—their cost-benefit balance is deeply skewed.

Different disorders, different glitches

For schizophrenia, the problem is information overload. Effort, reward, and probability all get tangled and can't be integrated into a coherent decision. It's like trying to juggle time, money, and cost at once, and the brain simply stalls.

For depression, the cost feels too heavy. The reward is still appealing, but every step toward it feels like climbing a mountain. A person may know seeing a friend would cheer them up, but the thought of getting dressed, leaving the house, and commuting is enough to stop them.

For bipolar disorder in a manic phase, the calculation flips backwards: things with low reward and high risk suddenly seem like a great deal, worth staying up nights to pursue.

How to help recalibrate the math

There's no one-size-fits-all fix. For some, making the reward concrete and tangible helps: 'Meeting a friend makes me feel less alone' motivates more than 'socialising is good for me.' For others, breaking tasks into smaller steps reduces the perceived cost.

Existing therapies are moving in this direction: some train people to anticipate and engage with positive experiences, others teach breaking activities into small steps, and still others strengthen attention and memory—all aimed at repairing the missing pieces in the calculation.

Next time someone seems lazy, don't rush to blame. Ask first: which step is hardest? Maybe it's not unwillingness—maybe the math in their head simply no longer adds up.