And, in fact, you can find that the lack of basic resources, material resources, contributes to unhappiness, but the increase in material resources do not increase happiness.

Csikszentmihalyi is drawing a distinction between material sufficiency and material accumulation. Severe deprivation—lack of food, shelter, safety, or basic stability—predictably undermines well-being, because it keeps attention locked on survival needs. But once those basics are met, additional wealth tends to yield diminishing returns in happiness: people adapt to improved circumstances, raise their expectations, and compare themselves to others, so the emotional “gain” from more possessions quickly fades. The remark aligns with his broader argument that lasting satisfaction is more reliably produced by meaningful engagement—especially experiences of “flow,” where attention is fully invested in challenging, intrinsically rewarding activity—than by consumption or status goods.