For a contact to receive your messages, several conditions must be met. Here's a checklist of things to verify to ensure your contacts are targeted when sending messages.
☑ The contact must be activated.
→ Verify the status of the contact
☑ The contact must be admissible to the channel used to send the message.
You can consult that info in a contact's profile: 
☑ The contact must have an opt-in (or an implied consent).
This opt-in must be linked to the communication type used by the message. You can see the consents of contacts in their profile: 
Note on implied consents: If a contact who had an implied consent and converted to an explicit consent unsubscribes, the implied consent won't be valid anymore.
☑ The contact must not be in quarantine or on the kill file.
→ Learn more about the quarantine
→ Learn more about the kill file
☑ The contact must have a valid email or a mobile number with a valid format.
→ Learn more about mobile phone formats accepted for SMS
☑ The contact must meet the criteria specified in the targeting used.
→ Learn more about the targeting tools
☑ The communication type must authorize the channel used for sending the message.
Verify that the right channel is selected when you create a communication type: