Here's how to fix the issue:

1. Remove <scope>provided</scope> after <artifactId>tomcat-embed-jasper</artifactId> in pom.xml (thanks user5819768 and Andy Wilkinson)

2. You should also move sayHello.jsp from /src/main/resources/META-INF/resources/WEB-INF/jsp/ to: src/main/webapp/WEB-INF/jsp/ (so that Tomcat can access it properly)

3. Restart IntelliJ (thanks Fabian McGibbon)

4. Maven > Execute Maven Goal > mvn clean install (thanks user5819768)