Google changes meta descriptions because it wants to show a sentence that best matches what someone is searching for. Even if you write a description, Google may pick a part of your page that fits the search better. This does not mean your description is bad, but it shows that search engines want to give users the clearest answer. Sometimes shorter sentences, including important words, or summarizing the page clearly can help Google use your description more. You do not have complete control, but writing clear summaries usually helps. What do you think?