The expansion of the function Ψ of three particles interacting with each other via the potentials <I>V</I>₁₂; <I>V</I>₁₃; <I>V</I>₂₃ in a complete set of the functions describing the motion of two particles coupled by a finite potential well <I>V</I>₁₂ (the complex particle) is considered. It is shown that in this expansion the population of the highest virtual states decreases with energy as \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{\varepsilon }{{\mathop \varepsilon \nolimits_n^3 }} $\end{document}. The system of integral differential equations for the bound state of three particles can be cut off (all the φ_<I>n</I> in (9) with ε_<I>n</I> > ε_<I>s</I>, where ε_<I>s</I> is rather large, may be neglected).