\documentclass[tikz]{standalone}
\usetikzlibrary{arrows.meta,shapes.symbols,matrix,positioning}
\begin{document}
- \begin{tikzpicture}[node distance=7em]
- \node (1) {no value};
+ \begin{tikzpicture}[node distance=7em,nodes={draw,minimum width=5em}]
+ \node (1) {no value};
\node (2) [right of=1] {unstable};
\node (3) [right of=2] {stable};
\draw [->] (1) -- (2);
\draw [->] (2) -- (1);
\draw [->] (2) -- (3);
- \draw [->] (1) to [out=20,in=160] (3);
+ \draw [->] (1.north east) to [out=25,in=155] (3.north west);
\end{tikzpicture}
\end{document}