nted in that consumer&#8217;s application logic.</p>
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<div class="paragraph">
<p>More importantly, such cases can arise at a later time. In fact, we must always expect changes to come, and never assume that we know our invariants. Even if we feel certain something is absolutely invariant, it often isn&#8217;t. All it takes is one counterexample, at some point in time, and your rigid structure will come to haunt you.</p>
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<div class="sect2">
<h3 id="make-changing-easy"><a class="anchor" hr