Think of it like mixing two pairs of dance partners in a room: when the copper ion pairs up with hydroxide, they form a solid bond that makes them sit down (precipitate) out of the liquid dance floor immediately.

Blue Precipitate = Copper Hydroxide (BPC - Blue Pale Copper)

In this double displacement (precipitation) reaction, the aqueous $\text{Cu}^{2+}$ ions from copper(II) sulfate combine with $\text{OH}^-$ ions from sodium hydroxide to form insoluble copper(II) hydroxide, $\text{Cu(OH)}_2$. The ionic equation for this reaction is $\text{Cu}^{2+}_{(\text{aq})} + 2\text{OH}^-_{(\text{aq})} \rightarrow \text{Cu(OH)}_{2(\text{s})}$.

For competitive exams, remember that $\text{Cu}^{2+}$ forms a pale blue precipitate of $\text{Cu(OH)}_2$ with $\text{NaOH}$, while $\text{Fe}^{2+}$ gives a dirty green precipitate of $\text{Fe(OH)}_2$ and $\text{Fe}^{3+}$ gives a reddish-brown precipitate of $\text{Fe(OH)}_3$.