Can you give a specific example of which words are supposed to be in bold? When I look at this post, I see the phrase Final words: in bold, down at the bottom.
You should note that by default, WordPress strips off HTML tags when it displays excerpts on the blog page. That is, on your blog page, you’ll notice that only the first 55 words of each article is displayed. That little bit is called an excerpt. Any formatting of the excerpt is stripped off. The reason is that if the “end tag” of a phrase isn’t within the first 55 words, then the appearance of the rest of the page might get screwed up. For example, let’s say that you’ve bolded the phrase Final words: and the word Final happens to be the 55th word, so that words: doesn’t get output in the excerpt. There’s what’s called an “end tag” which signals the end of a bolded phrase, and that end tag also will not get output, so the rest of the page will get bolded unintentionally. So what WordPress does is to strip off any HTML tags (which controls things like formatting, links, etc) before it displays the excerpt. Some themes will override that behavior, but at the risk of having the occasianal excerpt with HTML creating unintentional consequences.
WordPress does allow you to get around that. If you go and edit a post, if you scroll down, you should see a field labeled Excerpt. If you do not see such a field, click the Screen Options tab in the top right corner of the post editor, then check the box labeled Excerpt and the field should now be displayed. The Excerpt field allows you to create a manual excerpt, and WordPress will not strip off any formatting tags. This allows you to create any excerpt you want, any size you want. Note that some themes will ignore the Excerpt field, other themes will still strip off any formatting in the Excerpt field, you just have to experiment with your own theme.